Thursday, December 8, 2011

Dave Bolland and the Percentages

It's fun early in the season to click around on Behind the Net and look at the huge variation in on-ice shooting percentage and on-ice save percentage for hockey players around the league. For example, Detroit's Drew Miller has a .988 save percentage behind him this season. Matt D'Agostini is at .980, benefitting from Brian Elliott's completely unexpected early season star turn in St. Louis. In San Jose, Martin Havlat and Michal Handzus are at .966 and .964. At the other end of the scale, Ottawa's goalies have been absolutely ventilated (.795) with rookie Stephane DaCosta on the ice, explaining his team-worst -9 rating. Steve Downie, Marty Reasoner, Craig Adams and Matthew Lombardi are other regulars with on-ice save percentages still below .850.

There can be huge differences even between teammates playing in front of the same defencemen and goaltenders. Da Costa's teammate Jesse Winchester has a .940 save percentage behind him, meaning a shot has been 3.4 times more likely to go in the net with DaCosta on the ice than with Winchester. There's obviously no way a forward could have anything even close to that much of an impact on shot quality. It's a similar story in Detroit, where nobody scores with Drew Miller, Cory Emmerton (.955), Darren Helm (.955), or Tomas Holmstrom (.960) on the ice, but perennial Selke nominees Henrik Zetterberg (.891) and Pavel Datsyuk (.904) get lit up. Some small part of that is likely related to quality of competition, but with those kind of ranges and samples it is mostly luck.

The same type of thing can happen over a postseason as well, given that a typical Stanley Cup winner plays 22-26 games, and when it does it becomes more widely noticed and emphasized because the whole hockey world is paying attention. An example of a player who has been absolutely rocking the percentages in the playoffs lately is Chicago's Dave Bolland.

A huge part of both the 'Hawks Cup run in 2010 and their almost-comeback against the Canucks in their first round series in 2011 was the ability of the team's checking line to outscore strong opposition. Bolland attracted a lot of attention for his work, and a good portion of those accolades are indeed deserved. Bolland is a key member of the Blackhawks because of his ability to play tough minutes and has a big impact on Chicago's team depth when he is in the lineup. However, over the last three playoff series he and his linemates were outscoring at a completely unsustainable rate.

Copper 'n Blue counted scoring chances for the Blackhawks' series against San Jose and Philadelphia in 2010, as well as the first round matchup against Vancouver last season. With Bolland on the ice in the 14 games he played over that stretch, Chicago created 49 scoring chances and gave up 69 against at even strength. Given the difficulty of his minutes in terms of opposition and defensive zone starts, that's really not too bad for Bolland and his linemates. The curious part is that at the same time Bolland's plus/minus somehow managed to end up at +13.

Excluding shorthanded and empty net goals, Chicago outscored their opponents 16-5 with Bolland on the ice at even strength. That means the team scored in over 1 of 3 recorded chances (34.8%), while the scoring chance save percentage behind him has been an improbable .922. Depending on who is counting them, typical rates are 1 goal scored per 6 or 7 scoring chances. If you add up those two numbers, you get a way-off-the-charts scoring chance PDO number of 1270.

I often write about how much luck there is in the playoffs, and how randomness plays a big factor in what kind of labels get applied to players. When you have a player who is both playing well and getting lucky it becomes very tough for the opposition to overcome, and perhaps equally tough for sportswriters to avoid hyping up the impact of that particular player. Focusing strictly on results in terms of goals for and against, it is hard to deny that Bolland had a huge impact on the last three series for the Blackhawks. However, the underlying numbers show that it would be virtually impossible for that level of outscoring to continue, as the percentages needed to be extremely skewed in Bolland's favour for the numbers to come out the way they did. I wouldn't bet on his line outscoring Joe Thornton or the Sedins again in their next postseason matchup.

This season, Bolland's percentages have been trending in the exact opposite direction, which explains why he currently sits at -5. Despite facing the highest QualComp on the team and starting in his own zone 33.9% of the time, Bolland manages to almost break even in terms of Corsi and the Hawks have actually outshot their opponents 124-112 with him on the ice at 5 on 5. All that indicates that Bolland is playing extremely well, but unfortunately his PDO so far is just 943, mainly because the save percentage behind him is just .868, and as a result he has been outscored 17-10. In the long run it typically all evens out.

I hope you're right about Marty Reasoner. Many of my fellow Isles fans are ready to toss him overboard because "ZOMG he's supossed to be a defesnive speshulist!!!eleven!" But if he's just getting the worst of the goaltending stick there's hope that he will rebound somewhat to his historical results.

(FWIW - aside from DiPietro and the clearly-not-ready Anders Nilsson, the Isles have gotten very good goaltending. It'd be a real kick if that regressed to the mean at the same time as Reasoner's individual results improved.)

About Me

I'm Philip Myrland, goalie stats blogger since 2007 and former writer for Hockey Prospectus. I call myself a contrarian because I rely mainly on stats-based analysis, think large sample sizes are more important than "big saves" and prefer to rank goalies based on save percentage rather than team success. In other words, pretty much the mainstream views of the hockey analytics community, but I've grown attached to the handle and plan to keep it as long as broadcasters everywhere keep bringing up GAA and wins. If you have any questions or comments contact me by email (contrariangoaltender@gmail.com). You can also follow me on Twitter (@tcghockey).